Increasing concern over the quality of the environment has led to progressively stricter standards concerning environmental contaminants. The contamination of aquatic ecosystems has received particular attention from state and local governments as well as conservationists and sportsmen. One aquatic contaminant receiving particular attention from regulators and the public is lead shot from shotgun shells.
Lead shot contamination of aquatic ecosystems typically occurs where sportsmen fire shotguns over a body of water. The highest concentration of lead shot can be found in the waters offshore from gun clubs or other firing ranges. At these locations, clay targets are typically launched for trap or skeet shooting in a trajectory that causes lead shot fired at the targets to fall into a lake or other body of water. Because access to the waters offshore from the club usually is limited, this arrangement minimizes the chance for injury from lead shot fired at the clay targets.
Unfortunately, continued target shooting over a lake leads to a significant accumulation of lead shot on the bottom of the lake. Because the lead is relatively heavy, the lead shot becomes embedded in and mixed with the mud, silt, clay target material and other debris found on the bottom of the lake. As time goes on, the amount of lead on the bottom of the lake steadily increases until a significant concentration of lead shot is embedded in the lake bottom.
The accumulation of lead shot in the lake bottom can pose a significant environmental hazard. Lead, a heavy metal, is know to be a serious aquatic contaminant posing health hazards to humans and animals even when present at low levels.
The accumulation of lead shot also represents an unrealized economic resource. When the accumulation of shot is great enough, the contaminated bottoms might be more efficiently mined than other sources of lead found in nature, if a suitable recovery device existed. Reclamation of the lead shot from the lake bottom could, therefore, reduce environmental stress associated with other lead mining operations that are needed without the lead shot recovery.
While various mineral recovery devices are known in the art for recovering items such as gold particles, nuggets or flakes from a slurry of feed material, these devices typically are not designed to recover uniformly sized particles. Furthermore, most recovery devices known in the art cannot operate continuously, but instead must be shut down periodically to empty the recovered material from the device. These periodic shutdowns slow operations and can increase cost to the point where a lead shot recovery operation would be economically unfeasible.
Accordingly, a need exists for a device that can continuously recover lead shot or other generally uniform sized spherical pellets from a slurry of dredged feed material, thereby enhancing environmental quality and enabling the recycling of the lead so recovered.